Evaluating the impact of microorganisms in the iron plaque and rhizosphere soils of Spartina alterniflora and Suaeda salsa on the migration of arsenic in a coastal tidal flat wetland in China.

The microorganism in rhizosphere systems has the potential to regulate the migration of arsenic (As) in coastal tidal flat wetlands. This study investigates the microbial community in the iron plaque and rhizosphere soils of Spartina alterniflora (S. alterniflora) and Suaeda salsa (S. salsa), as two common coastal tidal flat wetland plants in China, and determines the impact of the As and Fe redox bacteria on As mobility using field sampling and 16S rDNA high-throughput sequencing. The results indicated that As bound to crystalline Fe in the Fe plaque of S. salsa in high tidal flat. In the Fe plaque, there was a decrease in the presence of Fe redox bacteria, while the presence of As redox bacteria increased. Thus, the formation of Fe plaque proved advantageous in promoting the growth of As redox bacteria, thereby aiding in the mobility of As from rhizosphere soils to the Fe plaque. As content in the Fe plaque and rhizosphere soils of S. alterniflora was found to be higher than that of S. salsa. In the Fe plaque, As/Fe-reducing bacteria in S. alterniflora, and As/Fe-oxidizing bacteria in S. salsa significantly affected the distribution of As in rhizosphere systems. S. alterniflora has the potential to be utilized for wetland remediation purposes.

Gilvirhabdus luticola gen. nov., sp. nov., a mesophilic and halophilic bacterium isolated from tidal flat sediment.

Two novel bacteria, MJ-SS3T and MJ-SS4, were isolated from tidal flat sediment sampled in Gochang, Republic of Korea. The isolates were Gram-stain-negative, aerobic, non-motile, rod-shaped, yellow-coloured, oxidase-positive, and catalase-positive. Strains MJ-SS3T and MJ-SS4 grew at 20-37 °C (optimum, 30 °C), at pH 6-8 (optimum, pH 7.0) and in the presence of 0-7 % (w/v) NaCl (optimum, 2.0 % NaCl). Strains MJ-SS3T and MJ-SS4 showed 99.9 % 16S rRNA gene sequence similarity. Phylogenetic analysis based on genome and 16S rRNA gene sequences indicated that strains MJ-SS3T and MJ-SS4 were affiliated with the family Flavobacteriaceae and most closely related to Formosa maritima 1494T (95.3 %), Hanstruepera flava NBU2984T (95.2 %), Yeosuana marina JLT21T (95.2 %), Meridianimaribacter flavus NH57NT (95.1 %), and Geojedonia litorea YCS-16T (95.1 %). The major respiratory quinone was menaquinone-6. The major identified polar lipids were phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, and amino lipids. The major cellular fatty acids of strain MJ-SS3T were iso-C15 : 1 G (24.6 %), iso-C15 : 0 (21.6 %), and iso-C17 : 0 3-OH (15.8 %). The genome length of strain MJ-SS3T is 3.1 Mbp (DNA G+C content, 32.5 mol%) and it has 2822 coding and 59 tRNA genes. The average amino acid identity and average nucleotide identity values, as well as biochemical, phylogenetic, and physiological characteristics, strongly supported the genotypic and phenotypic differentiation of strains MJ-SS3T and MJ-SS4 from other members of the family Flavobacteriaceae. Hence, strains MJ-SS3T and MJ-SS4 are considered to represent a novel species of a new genus in the family Flavobacteriaceae, for which the Gilvirhabdus luticola gen. nov., sp. nov. is proposed. The type strain is MJ-SS3T (=KCTC 102114T=KEMB 20189T=JCM 36595T), with reference strain MJ-SS4 (=KCTC 102115=KEMB 20190).

Evaluating the effects of laver cultivation on tidal flat erosion: Toward sustainable environmental practices.

The rapid expansion of laver (Porphyra yezoensis) cultivation on lower tidal flats has become integral to the local economy, yet it also raises concerns regarding its potential impact on the morphological evolution due to increasing human activities. This study utilizes integrated near-bed field measurements to assess morphological dynamics and quantify sediment erosion processes, highlighting the significant impact of laver harvest on tidal flat stability. Our results show that erosion and bed coarsening in the cultivated areas experienced a notable intensification immediately after harvest, with net erosion in cultivated areas reaching approximately -38.2 mm during the first tide post-harvest, markedly higher-more than an order of magnitude-compared to adjacent uncultivated areas. The erosion rate notably spiked with the average bed level change rate increasing to -13.8 × 10-4 mm/s, compared to a rate of +0.3 × 10-4 mm/s during the unharvest period. Subsequently, the cultivated areas entered a recovery phase with a deposition amount of +12.5 mm, while the net cumulative erosion thickness throughout the entire observation period was -25.2 mm. The cultivation method, characterized by consistent harvests every 10 days, means that even minor erosion from continuous harvests can escalate into significant degradation. This study suggests that long-term cultivation cycle practices may result in irreversible changes to the depositional environment, potentially jeopardizing the habitat viability and ecological function. Sustainable agricultural strategies, including site selection, infrastructure planning, monitoring environmental changes, ecological assessments and sustainable practices, are recommended to mitigate the negative impacts of cultivation on regional stability and preserve the coastal ecological balance.

Actinotalea lenta sp. nov., a novel actinomycete isolated from tidal flat sediment.

Two Gram-stain-positive, aerobic, oxidase- and catalase-negative, non-motile, and short rod-shaped actinomycetes, named SYSU T00b441T and SYSU T00b490, were isolated from tidal flat sediment located in Guangdong province, PR China. The 16S rRNA gene sequence similarity, average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between SYSU T00b441T and SYSU T00b490 were 99.3, 99.5 and 97.1 %, respectively. Strains SYSU T00b441T and SYSU T00b490 exhibited the highest 16S rRNA gene sequence similarities to Actinotalea ferrariae CF 5-4T (97.1 %/98.2 %), with ANI values of 74.01/73.88 % and dDDH values of 20.5/20.4 %. In the phylogenomic tree, the two isolates were affiliated with the genus Actinotalea. The genomes of strains SYSU T00b441T and SYSU T00b490 were 3.31 and 3.34 Mb, and both had DNA G+C contents of 72.8 mol%, coding 3077 and 3085 CDSs, three and three rRNA genes, and 53 and 51 tRNAs, respectively. Growth occurred at 15-40 °C (optimum, 28-30 °C), pH 4.0-10.0 (optimum, 7.0) and in the presence of 0-7 % (w/v) NaCl (optimum, 3 %). The major fatty acids (>10  %) of strains SYSU T00b441T and SYSU T00b490 were anteiso-C15 : 0 and C16 : 0. The major respiratory quinone was identified as MK-10(H4). The polar lipids of strains SYSU T00b441T and SYSU T00b490 were diphosphatidyl glycerol, phosphatidylglycerol, phosphoglycolipid, phosphatidyl ethanolamine, two phosphatidylinositol mannosides, two glycolipids and two phospholipids. Based on these data, the two strains (SYSU T00b441T and SYSU T00b490) represent a novel species of the genus Actinotalea, for which the name Actinotalea lenta sp. nov is proposed. The type strain is SYSU T00b441T (=GDMCC 1.3827T=KCTC 49943T).

Effects of major storms over a spit-tidal flat interaction system (Punta Rasa-Samborombón, Argentina).

Sandy coastal areas are very dynamic systems in which morphological changes occur over different time scales from hours to decades. However, it has been widely reported that major storms are the main responsible of the most significant changes in short to medium time scales. Major storms have been defined using a variety of environmental variables, but they are normally associated with high values of wave height, duration, return period and direction. Here, we aim to characterize types of major storms and to categorize associated morphological impacts over a complex coastal system. The study site, known as Punta Rasa, is located in the Samborombón bay in the outer part of the Río de La Plata estuary (Argentina) and corresponds to a zone of interaction between a large sandy spit and a backwash tidal flat system. Methods combine statistics of wave climate time-series, analysis of wave energy using nearshore numerical modelling (SWAN) and comparison of pre- and post-storm morphological changes by means of shoreline change detection and satellite images derived indexes (CoastSat Toolkit and NDWI index respectively). Results allowed to characterize four types of major storms impacting the study area: High-Energy Storms (HES), defined by an average storm wave below the 1 % exceedance (>2.6 m), Long-Lived Storms (LLS) represented by an exceedance of the 1 % of Du (>60 h), Storm Groups (SG) in which storm return period is <6 days and Northeastern moderate storms (NMS) defined by their eastern, onshore oriented direction. Under HES and NMS storms erosional areas are dominant over depositional, causing shoreline retreat, a growth of the end-spit and the increase on sand deposition on the back-barrier areas. Under LLS and SG storms, the morphological impact varies alongshore, with multiple erosional hotspots found along the shoreline accompanied by a general flattens of the end-spit system.

Measuring ecological quality status in low-diversity Arctic intertidal foraminiferal assemblages using a diversity-based index.

EcoQS assessment of the marine intertidal zone based on its fauna is challenging because the assemblages have a low diversity and consist of stress tolerant species. The new approach we propose is to pool foraminiferal diversity (effective number of species exp(H'bc)) across the whole intertidal zone including the salt marsh and tidal flat. In seven fjordheads studied in northern Fennoscandia, polycyclic aromatic hydrocarbon (PAH) concentrations indicated low levels of pollution (EcoQSPAH Excellent to Moderate). Jadammina or Balticammina dominated the salt marsh, Elphidium albiumbilicatum, Elphidium williamsoni, Elphidium clavatum, and Buccella frigida occurred in the tidal flat. Ovammina opaca thrived in both belts. While foraminiferal test abnormalities are often proposed to measure pollution impacts, we did not detect any correlation with PAHs. EcoQS based on foraminiferal diversity (EcoQSforam Excellent to Good) matched EcoQS based on PAHs suggesting that pooled foraminiferal diversity reliably measures intertidal EcoQS.

Genome-based classification of genera Halosegnis and Salella, and description of four novel halophilic archaea isolated from a tidal flat.

The current species of Halosegnis and Salella within the class Halobacteria are closely related based on phylogenetic, phylogenomic, and comparative genomic analyses. The Halosegnis species showed 99.8-100.0% 16S rRNA and 96.6-99.6% rpoB' gene similarities to the Salella species, respectively. Phylogenetic and phylogenomic analyses showed that Salella cibi CBA1133T, the sole species of Salella, formed a single tight cluster with Halosegnis longus F12-1T, then with Halosegnis rubeus F17-44T. The average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and average amino acid identity (AAI) values between Salella cibi CBA1133T and Halosegnis longus F12-1T were 99.2, 94.2, and 98.6%, respectively, much higher than the thresholds for species demarcation. This genome-based classification revealed that the genus Salella should be merged with Halosegnis, and Salella cibi should be a later heterotypic synonym of Halosegnis longus. Halophilic archaeal strains DT72T, DT80T, DT85T, and DT116T, isolated from the saline soil of a tidal flat in China, were subjected to polyphasic taxonomic characterization. The phenotypic, chemotaxonomic, phylogenetic, and phylogenomic features indicated that strains DT72T (= CGMCC 1.18925T = JCM 35418T), DT80T (= CGMCC 1.18926T = JCM 35419T), DT85T (= CGMCC 1.19049T = JCM 35605T), and DT116T (= CGMCC 1.19045T = JCM 35606T) represent four novel species of the genera Halorussus, Halosegnis and Haloglomus, respectively, for which the names, Halorussus caseinilyticus sp. nov., Halorussus lipolyticus sp. nov., Halosegnis marinus sp. nov., and Haloglomus litoreum sp. nov., are proposed.

Microbulbifer magnicolonia sp. nov., isolated from sediment of tidal flat located in Zhoushan, China.

A Gram-stain-negative, aerobic, motile with flagella and rod- or ovoid-shaped bacterium, designated GG15T, was isolated from tidal flat sediment sampled in Zhoushan, Zhejiang Province. Strain GG15T grew at 20-40 °C (optimum, 30 °C), at pH 5.5-9.5 (optimum, pH 7.0-8.0) and with 1.0-10.0 % (w/v) NaCl (optimum, 1.5 %). Colony diameters ranged from 1 to 3 mm within the first week, reaching a maximum of 6-7 mm after 15 days of cultivation. Strain GG15T exhibited highest 16S rRNA gene sequence similarity to Microbulbifer taiwanensis CCM 7856T (98.1 %), with similarity to other species within the genus Microbulbifer ranging from 97.8 to 93.8 %. Similarity values to other genera were below 93.8 %. Strain GG15T exhibited positive activity for ß-glucosidase, trypsin and chymotrypsin, whereas the reference strain showed negative activity. Chemotaxonomic analyses indicated that strain GG15T contained Q-8 as the sole respiratory quinone, C16 : 0 (9.1 %), iso-C15 : 0 (30.9 %) and iso-C11 : 0 3-OH (7.2 %) as the predominant fatty acids, and phosphatidylethanolamine, phosphatidylglycerol, three unidentified lipids, four unidentified glycolipids, one unidentified phospholipid, two unidentified aminolipids and two unidentified aminophospholipids as the main polar lipids. The genome of strain GG15T was 4 307 641 bp long, comprising 3861 protein-coding genes. The G+C content of strain GG15T was 61.5 mol% based on its genomic sequence. Strain GG15T showed low digital DNA-DNA hybridization (<70 %) and average nucleotide identity values (<95 %) with other Microbulbifer species. As a result, a novel species within the genus Microbulbifer, named Microbulbifer magnicolonia sp. nov., is proposed. The type strain is GG15T (MCCC 1K08802T=KCTC 8210T).

Integrated assessment of the natural purification capacity of tidal flat for persistent toxic substances and heavy metals in contaminated sediments.

Natural purification of pollutants is highly recognized as regulating ecosystem services; however, the purification capacity of tidal flats remains largely unknown and/or unquantified. A 60-day mesocosm transplant experiment was conducted in situ to assess the purification capacity of natural tidal flats. We adopted the advanced sediment quality triad approach, monitoring 10 endpoints, including chemical reduction, toxicity changes, and community recoveries. The results indicated that contaminated sediments rapidly recovered over time, particularly > 50% within a day, then slowly recovered up to âˆ¼ 70% in a given period (60 days). A significant early reduction of parent pollutants was evidenced across all treatments, primarily due to active bacterial decomposition. Notably, the presence of benthic fauna and vegetated halophytes in the treatments significantly enhanced the purification of pollutants in both efficacy and efficiency. A forecast linear modeling further suggested additive effects of biota on the natural purification of tidal flats, reducing a full recovery time from 500 to 300 days. Overall, the triad approach with machine learning practices successfully demonstrated quantitative insight into the integrated assessment of natural purification.

Evaluation of historical and future coastal wetland change in the Yellow and Bohai Seas using satellite images and a land use model.

Predicting the future distribution of coastal wetlands and characterizing changes in the area of wetlands between historical and future periods are important for the formulation of wetland conservation and management plans. Here, we used a cellular automata-Markov model and satellite images to simulate the future distribution of coastal wetlands under the business-as-usual scenario (BAU) and ecological protection scenario (EP) along the Yellow and Bohai Seas in China; we also explored historical (from 1990 to 2020) and future (from 2020 to 2050) changes in wetlands and the factors driving these changes. We found that the area of tidal flats gradually decreased because of increases in the area of saltpans, and the aquaculture area increased because of land reclamation and the invasion of Spartina alterniflora; most of the tidal flat area was fragmented into multiple small patches. If the current rate of degradation continues (BAU), the area of tidal flats will decrease by 21.25%, and the area of saltpans and aquaculture will increase by 13.83% and 21.25%, respectively. By contrast, under EP, the area of tidal flats will increase by 13.81%, and this increase will mainly stem from the conversion of areas with S. alterniflora (174.49 km2, 33.22%) to aquaculture areas (155.17 km2, 29.54%). Clear differences between historical and future periods were observed among Liaohe Estuary, Bohai Bay, Laizhou Bay, and the Yancheng-Nantong coasts. Land reclamation is the main factor inducing changes in the area of tidal flats, saltpans, and aquaculture in Liaohe Estuary, Bohai Bay, and Laizhou Bay. Land reclamation and the S. alterniflora invasion both affect the distribution of wetlands along the Yancheng-Nantong coasts.

Geographical variation of bacterial and ciliophoran communities in tidal flats in a continental archipelago.

In tidal flats, which are located at the transition zone between terrestrial and marine ecosystems, environmental factors such as temperature, sediment particle size, and tidal range exhibit geographic variation. Accordingly, the composition and structure of the microbial communities in the tidal flats are likely to vary in geographically different habitats. To clarify these differences with environmental factors causing them, we analyzed microbial communities consisting of bacteria and ciliates in sediments collected from nine tidal flats in geographical diverse region from Hokkaido to Kagoshima, Japan. The results confirmed that the community structures of bacteria and ciliophora in tidal flat sediments differed at the geographical scale of the Japanese archipelago. However, the variation could not be explained by the physical distance between the tidal flats nor by the differences in the trophic conditions among the tidal flats. Instead, the OTU richness of both the bacterial and ciliophoran communities was significantly related to the tidal range. The results also showed that bacteria and ciliophora tended to form similar communities among the tidal flats with similar median particle sizes. Furthermore, ciliophoran communities were similar among the tidal flats with similar bacterial communities. The results suggest that bacteria and ciliophora interact each other through trophic relationships or physical and chemical processes in the sediment habitats.

Seasonality in land-ocean connectivity and local processes control sediment bacterial community structure and function in a High Arctic tidal flat.

Climate change is altering patterns of precipitation, cryosphere thaw, and land-ocean influxes, affecting understudied Arctic estuarine tidal flats. These transitional zones between terrestrial and marine systems are hotspots for biogeochemical cycling, often driven by microbial processes. We investigated surface sediment bacterial community composition and function from May to September along a river-intertidal-subtidal-fjord gradient. We paired metabarcoding of in situ communities with in vitro carbon-source utilization assays. Bacterial communities differed in space and time, alongside varying environmental conditions driven by local seasonal processes and riverine inputs, with salinity emerging as the dominant structuring factor. Terrestrial and riverine taxa were found throughout the system, likely transported with runoff. In vitro assays revealed sediment bacteria utilized a broader range of organic matter substrates when incubated in fresh and brackish water compared to marine water. These results highlight the importance of salinity for ecosystem processes in these dynamic tidal flats, with the highest potential for utilization of terrestrially derived organic matter likely limited to tidal flat areas (and times) where sediments are permeated by freshwater. Our results demonstrate that intertidal flats must be included in future studies on impacts of increased riverine discharge and transport of terrestrial organic matter on coastal carbon cycling in a warming Arctic.

Pseudomonas aestuarii sp. nov., isolated from tidal flat sediment.

Two novel Pseudomonas strains, SA3-5T and SA3-6, were isolated from a tidal flat (getbol) in the Republic of Korea. Strains SA3-5T and SA3-6 were subjected to polyphasic characterization to determine their taxonomic affiliations. Cells were Gram-stain-negative, aerobic, rod-shaped and motile by using peritrichous flagella. Based on their 16S rRNA gene sequences, strains SA3-5T and SA3-6 exhibited a high degree of similarity (100 %) and were classified within the genus Pseudomonas. Furthermore, the closest related species to SA3-5T and SA3-6 were Pseudomonas taeanensis MS-3T (98.3 %). The ranges of average nucleotide identity and digital DNA-DNA hybridization values between SA3-5T and closely related species were 75.9-89.1% and 21.3-38.7%, respectively, both of which being below the thresholds for delineating novel strains. Strain SA3-5T and SA3-6 contained C16 : 1 ω6с and/or C16 : 1 ω7с (summed feature 3), C16 : 0 and C18 : 1 ω6с and/or C18 : 1 ω7с (summed feature 8) as the major fatty acids. The predominant respiratory quinone was Q-9. The DNA G+C content of strain SA3-5T was 62.5 mol%. Based on their combined phenotypic, chemotaxonomic and phylogenetic characterisitics, strains SA3-5T and SA3-6 represent a novel species of the genus Pseudomonas for which the name Pseudomonas aestuarii sp. nov. is proposed. The type strain is SA3-5T (=KCTC 92395T=JCM 35697T).

Tenacibaculum tangerinum sp. nov., isolated from a tidal flat sediment.

An orange-coloured bacterium, designated as strain GRR-S3-23T, was isolated from a tidal flat sediment collected from Garorim Bay, Chuncheongbuk-do, Republic of Korea. Cells of GRR-S3-23T were aerobic, Gram-stain-negative, rod-shaped and motile. GRR-S3-23T grew at 18-40 °C (optimum, 30 °C), pH 7.0-9.0 (optimum, pH 7.0) and with 2-4 % NaCl (optimum, 2-3 % w/v). Results of 16S rRNA gene sequence analysis indicated that GRR-S3-23T was closely related to Tenacibaculum aiptasiae a4T (97.6 %), followed by Tenacibaculum aestuarii SMK-4T (97.5 %), Tenacibaculum mesophilum MBIC 1140T (97.4 %), Tenacibaculum singaporense TLL-A2T (97.3 %), Tenacibaculum crassostreae JO-1T (97.2 %),and Tenacibaculum sediminilitoris YKTF-3T (97.1 %). The average amino acid identity values between GRR-S3-23T and the related strains were 86.8-72.8 %, the average nucleotide identity values were 83.3-74.1 %, and the digital DNA-DNA hybridization values were 27.0-19.6 %. GRR-S3-23T possessed menaquinone-6 (MK-6) as major respiratory quinone and had summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c, 20.6 %) and iso-C15 : 1G (10.8 %) as major fatty acids (>10.0 %). The polar lipid profiles of GRR-S3-23T contained phosphatidylethanolamine, one unidentified aminolipid, one unidentified aminophospholipid, three unidentified lipids, one unidentified glycolipid and four unidentified phospholipids. The DNA G+C content of GRR-S3-23T was 33.7%. On the basis of the results of the polyphasic analysis involving phylogenetic, phylogenomic, physiological and chemotaxonomic analyses described in this study, GRR-S3-23T is considered to represent a novel species within the genus Tenacibaculum, for which the name Tenacibaculum tangerinum is proposed. The type strain is GRR-S3-23T (=KCTC 102029T=KACC 23271T=JCM 36353T).

Robiginitalea aestuariiviva sp. nov. isolated from sediment of tidal flat located in Zhejiang, PR China.

A Gram-stain-negative, strictly aerobic and rod- to coccoid-shaped bacterium, designated as strain M366T, was isolated from coastal sediment of Jiaoshanjiao, Zhejiang Province, PR China (121°54' E 29 °38' N). The draft genome of strain M366T was 3 225 479 bp long (with 55.6 mol% G+C content) and assembled into four contigs. The N50 value was 563 270 bp and the genomic completeness and contamination were estimated to be 99.34 and 0.05 %, respectively. Colonies of strain M366T were yellow-orange, 1 mm in diameter, round, opaque, smooth and convex after incubation on marine agar at 30 °C for 3 days. Cells were catalase-positive but oxidase-negative. Strain M366T was observed to grow at 20-40 °C (optimum, 30 °C), pH 5.5-9.0 (optimum, pH 6.5-7.0) and with 0.5-8.0 % (w/v) NaCl (optimum, 2.5 %). Strain M366T shown highest 16S rRNA gene sequence similarity of 98.1 % to Robiginitalea sediminis O458T, 95.6-95.9 % to other type strains of the genus Robiginitalea and below 93 % to other genera. The average nucleotide identity and digital DNA-DNA hybridization values between strain M366T and its closely related Robiginitalea species were 71.1-75.9 % and 17.5-19.0 %. Menaquinone-6 was the only respiratory quinone. The major fatty acids (>10 %) were iso-C15 : 0, iso-C17 : 0 3-OH and summed feature 1 (iso-C15 : 1 h and/or C13 : 0 3-OH). The main polar lipids included phosphatidylethanolamine, two unidentified phospholipid, two unidentified aminophospholipid, one unidentified glycolipid and five unidentified lipids. According to the above results, Robiginitalea aestuariiviva sp. nov. is proposed and the type strain is M366T (=KCTC 92866T=MCCC 1K04524T=CGMCC 1.61708T).

Distribution characteristics and influencing factors of soil organic carbon in tidal flat wetland of central Jiangsu, China.

We measured winter and summer soil organic carbon (SOC) contents in two typical coastal wetlands, the Spartina alterniflora salt marsh and the non-vegetation mudflat, on the south side of the Chuandong River Estuary in Yancheng, Jiangsu Province. We investigated the spatiotemporal variations of soil organic carbon contents and its driving factors. The results showed that SOC content ranged from 0.75 to 2.38 g·kg-1 in the mudflat area and from 2.07 to 18.59 g·kg-1 in the S. alterniflora salt marsh area, showing a decreasing trend towards the sea. The SOC content in the S. alterniflora salt marsh area was approximately 2.5 to 3.5 times of that in the mudflat area. Within a depth range of 1 m, there was no vertical variation in SOC content in the mudflat area, but an increasing and then decreasing pattern in the S. alterniflora marsh area with the peak occurring in the depth range of 20 to 30 cm. Soil organic carbon content exhibited significant seasonal difference, with higher value in summer than in winter. The summer SOC content was 5% to 10% higher than that in winter in the S. alterniflora marsh area, while it was 43% higher in summer than in winter in the mudflat area. In the S. alterniflora marsh area, soil organic carbon content was positively correlated with soil moisture and salinity, but negatively correlated with sediment particle size. In contrast, there was no significant correlation between soil organic carbon content and soil physicochemi-cal factors in the mudflat area. Those results indicated that the correlation between various soil physicochemical factors and SOC is established on the basis of vegetation cover in coastal wetlands. Our findings could provide valuable insights for the conservation of blue carbon ecosystems in coastal wetlands in China.

Spatial distribution of antibiotics and antibiotic resistance genes in tidal flat reclamation areas in China.

Tidal flat areas are important resources for land development and are becoming antibiotic resistance receivers that trigger major health concerns. The spatial distributions of forty-nine antibiotics, nine antibiotic resistance genes (ARGs), one mobile gene element (MGE) gene, and nine available metals in the soils and sediments along the coastlines of the Yellow Sea in China were quantified. Hierarchical linear model analysis was used to explore relationships between the antibiotics and ARGs across multiple effects resulting from human activities and environmental factors. Fish farm sediments and farmland soils showed high levels of quinolones (QNs) (maximum 637 ng·g-1), sulfonamides (SAs) (maximum 221 ng·g-1), and corresponding ARGs. Significant positive correlations (P from 5.47 × 10-14 to 0.0487) were observed between the antibiotics (QNs, SAs, and chlortetracycline) and their corresponding ARGs (qnrA, qnrD, aac(6')-Ib-cr, dfrA, sul2, and tetA), indicating the selective pressure from antibiotics in soils and sediments. Nine available metals had positive correlations with at least one ARG, indicating heavy metal pollution could enhance the ARGs. Sheep and poultry husbandry and marine aquaculture contribute the most to the antibiotic resistance in the coastlines. In conclusion, antibiotic pollutions have promoting effects at sub-inhibitory concentrations and more attention should be given to inhibit the enrichment of ARGs during tidal flat reclamation processes. The study also suggests the induction effects from metal pollutions, MGE spread, and the antibiotic pollutions from the usage in livestock and aquaculture.

Unraveling the interplay between antibiotic resistance genes and microbial communities in water and sediments of the intensive tidal flat aquaculture.

Tidal flats are formed valuably resources by the interaction of terrestrial and marine processes. Aquaculture on tidal flats has brought significant economic profits, but the over usage of antibiotics has resulted in the prevalence antibiotic resistance genes (ARGs) which pose serious threats to ecosystems. However, ARG abundances and bacterial community assemblies in the overlying water and sediments of tidal flat aquaculture areas have not been fully explored. Thus, antibiotic concentrations, ARG abundances, microbial communities and the influences of environmental factors in the Jiangsu tidal flat aquaculture ponds were investigated using high-throughput sequencing and qPCR. The concentrations of antibiotics at sampling ranged from not detectable to 2322.4 ng g-1, and sulfamethazine and ciprofloxacin were the dominant antibiotics. The sul1 and sul2 abundances were highest and the ARG abundances were higher in sediment than in water. Meanwhile, bacterial community diversities and structures were significantly different (P < 0.05) between water and sediment samples. Network analysis identified Sphingomonadacear, Pseudomonas, and Xanthobacteraceae as potential ARG-carrying pathogens. A positive correlation between ARGs and intI1 indicated that horizontal gene transfer occurred in water, while antibiotics and TN significantly influenced ARG abundances in sediment. Neutral modeling showed that deterministic and stochastic processes contributed most to the bacterial community assemblies of water and sediment samples, respectively. This study comprehensively illustrates the prevalence of ARGs in intensive tidal flat aquaculture regions and provides an effective foundation for the management of antibiotics usage.

Populations of the Intertidal Crab Macrophthalmus banzai are Not Grouped by Latitude: Taiwan Population is Genetically Closer to the Populations in the Japanese Mainland Than the Ryukyu Islands.

Macrophthalmus banzai is an intertidal crab species of Macrophthalmidae inhabiting muddy tidal flats in the northwestern Pacific. A previous study on the population genetic structure of Japanese M. banzai based on the mitochondrial COI gene sequences revealed the presence of two genetically distinguished groups, i.e., the northern group (Honshu, Shikoku, and Kyushu Islands) and the southern group (the Ryukyu Islands). In the present study, we newly determined the COI gene sequences of M. banzai collected from Taiwan and conducted population genetic analyses of these sequences together with Japanese sequences obtained from GenBank to reveal the genetic relationship of this species between Japan and Taiwan. The SAMOVA and pairwise ΦST analysis showed that the Taiwan population is more closely related to the northern group than the southern group. This indicates that the populations of M. banzai are not genetically differentiated by latitude but probably by the pathway of the Kuroshio Current, resulting in the isolation of the population in the Ryukyu Islands. Such a pattern is consistent with the population genetic structure of the fiddler crab Tubuca arcuata shown by a previous study, whereas the pattern differs from those of other intertidal invertebrates. The difference in the larval durations may have influenced the difference in population genetic structures among species. The present study provides a further case of the genetic structure of intertidal species that are not simply regulated by geographic distances.

Sources of Polycyclic Aromatic Hydrocarbons in Fecal Pellets of a Marphysa Species (Annelida: Eunicidae) in the Yoro Tidal Flat, Japan.

The fecal pellets of Marphysa sp. E sensu Abe et al. (2019) (Annelida, Eunicidae) living in the Yoro tidal flat (Ichihara, Chiba, Japan) contain high levels of polycyclic aromatic hydrocarbons (PAHs), and the concentrations rapidly decrease over time. To investigate the origin of the high-concentration PAHs in the fecal pellets and food sources of the worms, the PAH concentrations, carbon and nitrogen stable isotope ratios (δ13C and δ15N), total organic carbon, and total nitrogen for two types of sediment (sands and reduced muds), fecal pellets, and the body of the worms were determined. The PAH concentrations and chemical properties of the fecal pellets were similar to those of the reduced muds (20-30 cm sediment depth). The δ13C, δ15N, and C/N values of reduced muds were the same as the typical values of terrestrial C3 plants, suggesting that reduced muds were derived from terrestrial plants. These data indicated that the worms selectively take up reduced muds containing high levels of PAHs. The δ13C and δ15N values of the worm bodies indicated that the worms did not use the organic carbon derived from terrestrial C3 plants as primary nutrition. Taking into consideration their selective uptake of reduced muds, excretion, and subsequent rapid decrease of PAHs in the fecal pellets, the worms could contribute to the remediation of chemical pollutants in the tidal flat sediments.